As to the idea of limited variety, propounded by Isidore Geoffroy, we can only see in it an unfortunate restriction of his father’s theory,--one of those errors into which even the most judicious minds are liable to fall. Limited! Does he mean that there is a point where these variations stop, and consequently a point where they have commenced? Does he mean that some neighbouring animal species are derived from a given prototype, similar to themselves, and without any antecedents in the organic world? This is to return to Cuvier! Limited! Does he mean that the modifications will not be considerable in the present state of things, on account of this present state being more or less modified? It comes to nothing directly we admit variety as a consequence of the medium. Étienne Geoffroy was led by this kind of idea, when, limiting his view to the short period of historical time, and thinking he had discovered that our present climates do not sensibly alter existing species,[308] he asked, “if there had not been on the earth revolutions and disturbances of so vast a character that their influence may not have been enormous; whilst in our days, changes may have been according to the power of their effects, that is to say, almost nothing.” And he explained everything by this convenient theory of geological floods. Before going farther, let us consider what we ought to think about the disturbances of the terrestrial globe thus invoked by Étienne Geoffroy. Now, to our mind, we have no authentic proof that the past of our planet has really been marked by such frightful revolutions, and geology does not make the tradition as clear as some have desired. We think, although this is not the place to prove it, that if the changes which have happened to the surface of the globe have been considerable, they ought to be proportionally _weak_, resulting less from sudden and powerful efforts than from those small and continuous actions[309] in which nature puts forth its most formidable energies, but the progress of which is not to be measured by the memory of man. In general, our mind seizes but badly the notion of duration beyond certain limits. It is not the same with the notion of force. Hence, the belief in floods. In the presence of gigantic effects, the mind, in the appreciation of the movers of this effect, has done what we have done every day in mechanics. “It has changed mind into force.” It is certain that weak but continuous forces (everywhere, however, the most powerful) have been able to play a grander part in the history of our globe, than these disturbances which we are in the habit of seeing everywhere.